We have been studying a subdivision of the pulvinar to determine its role in selective visual attention. Monkeys and humans were trained to fixate on a spot of light and respond to the onset of a peripheral light. Reaction times for both species were faster when the target was preceded by a cue correctly indicating the location of the target; reaction times were slowed by invalid cues. These data suggest that the cue shifts attention to one side and speeds or slows responses with valid or invalid cues, respectively. Since our electrophysiological recordings suggested that the beta subdivision of the lateral pulvinar is related to visual attention, we injected drugs into this area in two monkeys in an attempt to change the monkeys' attentional behavior. GABA is a transmitter in this part of the brain, and we used drugs which either increased or decreased GABA levels. Increased levels of GABA were associated with slowed attention shifts to the contralateral side; decreased GABA levels were associated with speeded attentional shifts. These studies support a role for this area of the brain in selective visual attention.